JP7565686B2 - Conductive Paste - Google Patents

Description

The present invention relates to a conductive paste. More specifically, the present invention relates to a conductive paste suitable for forming unfired electrodes of ceramic electronic components.

As electronic devices become smaller and more powerful, there is a demand for ceramic electronic components mounted in them to also become smaller and more powerful. In particular, with vehicles becoming more connected, electronic components for use in vehicles are required to be not only smaller, but also more heat-resistant and reliable.

Ceramic electronic components generally have a component body and external electrodes formed on a pair of opposing end faces of the component body, and are mounted on a substrate by soldering the external electrodes to the substrate. Here, it is known that in in-vehicle electronic devices and the like, substrates on which ceramic electronic components are mounted can bend due to sudden temperature changes. At this time, since the thermal expansion coefficients of the ceramic electronic components and the substrate are different, there is a concern that the ceramic electronic components mounted on the substrate will be subjected to thermal shock, and the brittle ceramic electronic components will be damaged by cracks, etc. Therefore, a conductive film (resin electrode layer) containing a resin component is interposed between the external electrodes of the ceramic electronic components, and the resin electrode layer is used to mitigate the thermal shock applied to the ceramic electronic components (see, for example, Patent Documents 1 and 2). It has also been proposed to mount (bond) ceramic electronic components to a substrate using a conductive paste containing a resin component instead of solder (see, for example, Patent Document 3).

JP 2018-104820 A Special table 2018-516755 publication JP 2006-073812 A

By the way, in the conventional conductive paste for forming a conductive film containing a resin component, a thermosetting resin such as an epoxy resin or a urethane resin is used as the resin component. However, these epoxy resins and urethane resins have a heat resistance of about 150°C when used continuously at high temperatures, and there is a problem that the resin component deteriorates when exposed to a temperature environment higher than this. In addition, super engineering plastics (super engineering plastics) such as polytetrafluoroethylene and PEEK (polyether ether ketone) resin are known as resins with high heat resistance. However, there is a problem that the adhesion of the highly heat-resistant super engineering plastics to the substrate is insufficient. For example, for a conductive film used in electronic components that may be exposed to a high-temperature environment for a long time, such as ceramic electronic components for automobiles, it is desirable to have both high heat resistance of about 180°C to 280°C and adhesion.

The present invention was made in consideration of these points, and its purpose is to provide a conductive paste capable of forming a conductive film containing a resin component that has both heat resistance and adhesive properties.

The present inventors have investigated from various angles the conductive film formed from a conductive paste containing a super engineering plastic as a resin component, which can be used for a long period of time at high temperatures of 150°C or more. As a result, it was found that a conductive film containing a super engineering plastic alone as a resin component has too rigid film properties to obtain the desired adhesiveness. Therefore, the present inventors have focused on polyimide resin, which has extremely high heat resistance among super engineering plastics, and have conducted extensive research with the aim of blending different resin components into this polyimide resin to impart flexibility to the conductive film formed and improve its adhesiveness to the substrate. As a result, they have found that the adhesiveness of the conductive film can be improved by blending a resin component that was thought to have poor adhesiveness into a polyimide resin, and have completed the present invention.

That is, the conductive paste disclosed herein contains conductive particles, a resin component, and an organic solvent. The resin component contains polyimide resin and silicone resin, and the ratio of polyimide resin to silicone resin is adjusted to be 95:5 to 50:50 by mass.

According to the above configuration, a conductive paste capable of forming a conductive film having excellent adhesiveness exceeding that exhibited in a conductive film containing these resins alone is realized by the synergistic effect of the polyimide resin and the silicone resin. Although the details are not clear, the polyimide resin has a rigid main skeleton based on its chemical structure, and in addition to being difficult to soften under temperature conditions, it is difficult to spread wetly on the substrate. In contrast, it is considered that by dispersing the silicone resin in the polyimide resin, the molecular structure of the polyimide is moderately disturbed, and the effect of the polyimide resin being easily spread wetly on the substrate along with the softening of the silicone resin is exhibited. As a result, the conductive film obtained by drying this conductive paste is suitably enhanced in high heat resistance (e.g., about 180°C or more and 280°C or less) and adhesiveness (e.g., 4N/ ^mm2 or more). This provides a conductive paste capable of forming a conductive film having high heat resistance and good adhesiveness to the substrate.

In a preferred embodiment of the conductive paste disclosed herein, the silicone resin is an addition-curing silicone resin, which allows the conductive film formed from the conductive paste to have an excellent adhesive strength of, for example, 6 N/mm2 or ^more .

In a preferred embodiment of the conductive paste disclosed herein, the silicone resin is a resin-based silicone resin. With this configuration, the conductive film formed from the conductive paste can have an adhesive strength of, for example, 6 N/mm2 or ^more , which is excellent in adhesiveness.

In a preferred embodiment of the conductive paste disclosed herein, the resin component is contained in an amount of 10 parts by mass or more and 30 parts by mass or less when the conductive particles are taken as 100 parts by mass. This makes it possible to suitably form a conductive film with excellent electrical conductivity.

In a preferred embodiment of the conductive paste disclosed herein, the conductive particles contain at least one of nickel, platinum, palladium, gold, silver, and copper. This configuration also makes it possible to preferably form a conductive film with excellent electrical conductivity.

As described above, the conductive paste disclosed herein can form a conductive film that has both high heat resistance and adhesiveness. Such properties can be fully utilized by using it to form, for example, a resin electrode layer contained in an external electrode of a ceramic electronic component used in an environment where vibration occurs at high temperatures, or a conductive resin for bonding. For example, in a preferred embodiment of the conductive paste disclosed herein, it is used to form a resin electrode layer of an external electrode of a ceramic electronic component.

From another perspective, the ceramic electronic component disclosed herein comprises a component body including a ceramic base and an internal electrode disposed within the ceramic base, and an external electrode provided on the surface of the component body. The external electrode at least partially includes a conductive film (typically a dry film) formed from any of the conductive pastes described above. This realizes a highly reliable ceramic electronic component that is less likely to peel off or break due to vibrations from the rotating parts, even in high-temperature environments.

FIG. 1 is a cross-sectional view illustrating a multilayer ceramic capacitor according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the blending amount of silicone resin in a conductive paste according to one embodiment and the adhesiveness of a resin electrode layer.

The following describes preferred embodiments of the present invention. Note that matters other than those specifically mentioned in this specification (e.g., the configuration of the conductive paste) that are necessary for implementing the present invention (e.g., the method for preparing the conductive paste and the configuration of the ceramic electronic components) can be understood as design matters of a person skilled in the art based on the prior art in the field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the field.

In the following description, the unfired film-like body obtained by applying a conductive paste to a substrate and drying at a temperature below the thermal decomposition temperature of the resin component contained in the conductive paste (for example, below 300°C) is referred to as a "conductive film." In this specification, "conductive film" includes the meanings of "resin electrode film" and "conductive resin for bonding." In addition, in this specification, the notation "A to B" indicating a numerical range means greater than or equal to A and less than or equal to B.

<Conductive paste>
The conductive paste disclosed herein (hereinafter, sometimes simply referred to as "paste") can form a conductive film by drying. The conductive paste disclosed herein contains conductive particles (A), a resin component (B), and an organic solvent (C). The conductive film (typically a resin electrode film or a conductive resin for bonding) formed from this conductive paste contains conductive particles (A) and a resin component (B). In this specification, the term "paste" includes a composition, an ink, a slurry, a suspension, and the like. Each component will be described in order below.

(A) Conductive Particles The conductive particles are typically prepared in the form of powder. The conductive particles are a component that imparts electrical conductivity to the conductive film obtained after drying. The type of conductive particles is not particularly limited, and one or more types of commonly used conductive particles can be appropriately used according to the application. A preferred example of the conductive particles is a conductive metal powder. Specifically, examples include simple metals such as nickel (Ni), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), copper (Cu), ruthenium (Ru), rhodium (Rh), iridium (Ir), osmium (Os), and aluminum (Al), as well as mixtures and alloys thereof.

For example, in applications such as forming resin electrode films for multilayer ceramic electronic components and conductive resins for bonding, high electrical conductivity is required without firing. Examples of such highly conductive metals include nickel, platinum, palladium, silver, and copper. Of these, silver and silver alloys are preferred because of their chemical stability and excellent heat resistance.

The properties of the particles that make up the conductive particles, such as the size and shape of the particles, are not particularly limited as long as they fall within the minimum dimension of the cross section of the desired conductive film (typically the thickness and/or width of the conductive film). The average particle diameter of the conductive particles (the particle diameter that corresponds to the cumulative 50% from the small particle diameter side in the volume-based particle size distribution determined by a laser diffraction type particle size distribution measuring device; the same applies below) is preferably approximately several tens of nm to several tens of μm, for example 1 μm to 10 μm.

The shape of the conductive particles may be, for example, spherical or non-spherical. The non-spherical shape may be, for example, plate-like, scale-like, flake-like, or amorphous. From the viewpoint of facilitating an increase in the packing density of the conductive particles, for example, spherical conductive particles having an aspect ratio of 1.2 or less, preferably 1.15 or less, for example, 1.1 or less, can be preferably used. From the viewpoint of facilitating an increase in the contact area of the conductive particles, for example, non-spherical conductive particles having an aspect ratio of more than 1.2, preferably 1.3 or more, 1.5 or more, for example, 1.7 or more, and more preferably 2 or more can be used. From the viewpoint of synergizing the above effects, the conductive particles may be a mixture of spherical and non-spherical. As a result, when the solvent is removed from the paste by drying, the multiple conductive particles are in favorable contact with each other, and the electrical conductivity of the conductive film can be increased. The aspect ratio is a value calculated based on electron microscope observation by (long side ÷ short side) of the smallest circumscribing rectangle of the conductive particles.

The content of the conductive particles (A) is not particularly limited, but it is preferable that the content is approximately 30% by mass or more, typically 40 to 95% by mass, for example 50 to 85% by mass, when the entire conductive paste is taken as 100% by mass. By satisfying the above range, a conductive film with high electrical conductivity and density can be suitably realized. In addition, the handleability of the paste and the workability during film formation can be improved.

(B) Resin Component The resin component contains a polyimide resin (B1) and a silicone resin (B2).
(B1) Polyimide resin A polyimide resin is a polymer containing an imide bond in the repeating unit. A polymer is a molecule having a large molecular weight (e.g., a weight average molecular weight of 1000 or more) and has a structure composed of a large number (e.g., 5 or more) of repeating units (same as repeating units) substantially or conceptually obtained from molecules having a small molecular weight (e.g., a weight average molecular weight of 500 or less). A polyimide resin typically contains a repeating unit structure represented by the following formula (1). Here, R and R' in the formula are independently any organic functional group or oxygen atom.

A polyimide resin is typically a crystalline or non-crystalline polymer in which a repeating unit containing an imide bond constitutes the main chain. From the viewpoint of forming an electrode with higher adhesion, a crystalline polymer may be used. Also, from the viewpoint of providing higher heat resistance, a non-crystalline polymer may be used. Furthermore, in the state of a homopolymer, the polyimide resin may have a heat resistance temperature of 250°C or higher, for example, a glass transition point of 200°C or higher, preferably 210°C or higher, and more preferably 220°C or higher. In a polyimide resin, the ratio of the number of moles of repeating units containing imide bonds to the number of moles of all repeating units is usually 50% or higher (for example, 50% to 95%), preferably 65% or higher, more preferably 75% or higher, for example 85% or higher. For example, all repeating units may be composed of units containing aliphatic or cyclic aliphatic groups.

In polyimide resins, the type of repeating unit of imide bonds is not particularly limited. Examples of units containing imide bonds include, but are not limited to, s-ODPA, i-ODPA, a-ODPA, 2,2'-BAPB, 4,4'-BAPB, 1,5-NBOA, 2,3-NBOA, 3,3'-ODA, 4,4'-ODA, PMDA, BPDA, BPADA, BTDA, BAFL, 2,2-TFMB, 1,3,3-APB, 1,3,4-APB, DDS, etc. Any one of these may be used alone, or any combination of two or more may be used.

Such polyimide resins can be obtained by selecting from polyimide materials manufactured by, for example, JFE Chemical Corporation, Kyocera Chemical Corporation, SABIC Corporation, and PI Technical Research Institute that satisfy the above characteristics according to the desired application.

(B2) Silicone Resin As the silicone resin, among the polymer organic compounds having a main skeleton based on a siloxane bond (Si-O-Si) consisting of silicon (Si) and oxygen (O), a polymer organic compound containing a branched chain can be used. That is, among the siloxane compounds called so-called silicone oil, silicone rubber, and silicone resin, silicone rubber and/or silicone resin, excluding linear silicone oil, may be used. Silicone rubber is an elastomer with a low degree of branching (degree of cross-linking) and rubber elasticity at room temperature (e.g., 25°C). Silicone resin has a high degree of branching (degree of cross-linking) and has a developed three-dimensional polymer structure. Of the silicone rubber and the silicone resin, it is more preferable to use the silicone resin as the silicone resin. The silicone resin may be solid or liquid at room temperature (e.g., 25°C).

The silicone resin forming the main skeleton may be, for example, a polysiloxane containing a siloxane unit represented by the general formula: HO[-Si(R) ₂ O-] _n H, where R is hydrogen or any functional group; a polyalkylsiloxane in which R is any alkyl group; or a polymer obtained by polymerizing a siloxane unit with a silicon-containing monomer different therefrom. Specifically, examples of the silicone resin include polydialkylsiloxanes such as polydimethylsiloxane, polydiethylsiloxane, and polymethylethylsiloxane, polyalkylarylsiloxane, and poly(dimethylsiloxane-methylsiloxane). A particularly suitable polymer constituting the main skeleton may be, for example, polydimethylsiloxane. The silicone resin may also be a linear modified silicone in which other substituents such as polyether groups, epoxy groups, amine groups, carboxyl groups, alkyl groups, and hydroxyl groups have been introduced into the side chains, ends, or both of the main skeleton.

It is also known that silicone resins are classified into addition-curing silicone resins and dehydration-condensation-curing silicone resins. Of these, dehydration-condensation-curing silicone resins may adversely affect the electrode film in which water is formed as a reaction by-product. Therefore, although not necessarily limited to this, it is more preferable that the silicone resin be an addition-curing silicone resin.

Such silicone resins can be obtained by selecting, for example, silicone resins or silicone rubbers manufactured by Shin-Etsu Chemical Co., Ltd. or Wacker Asahi Kasei Silicone Co., Ltd. that satisfy the above characteristics according to the desired application.

Polyimide resin and silicone resin can improve the adhesiveness of polyimide resin by blending even a small amount of silicone resin into polyimide resin. However, for example, in a conductive paste used to form a conductive film having high adhesiveness of 4 N/mm2 or ^more , when the total of polyimide resin and silicone resin is 100 mass%, the proportion of silicone resin may exceed 2 mass%, may be 3 mass% or more, and more preferably 5 mass% or more, 7 mass% or more, for example 8 mass% or more, or even 10 mass% or more. However, blending silicone resin at an excessive proportion is not preferable because it may inhibit the excellent properties of polyimide resin. The proportion of silicone resin is preferably less than 60 mass%, and is preferably 50 mass% or less, for example 40 mass% or less, 30 mass% or less, or even 25 mass% or less.

In addition, the higher the ratio of the (B) resin component to 100 parts by mass of the (A) conductive particles, the more the conductive film can absorb and reduce external vibrations and thermal shocks. The ratio of the resin component may be, for example, 3% by mass or more, and more preferably 5% by mass or more, 8% by mass or more, for example 10% by mass or more. However, if the ratio of the resin component is excessive, it is not preferable because the resin component present between the conductive particles may become a resistance. The ratio of the resin component may be, for example, 30% by mass or less, preferably 25% by mass or less, and may be, for example, 20% by mass or less.

As described above, this conductive paste must contain polyimide resin and silicone resin. On the other hand, block copolymers of polyimide resin and silicone resin, in which a silicone structure is introduced into the polyimide chain, are also available on the market. This silicon-modified polyimide block copolymer can be understood as a polyimide that is given adhesion and flexibility. However, if polyimide resin and silicone resin are copolymerized, there is a major disadvantage that the heat resistance is impaired in the polymerized portion. Therefore, it is preferable that the polyimide resin and silicone resin are included in the conductive paste as a blend of simple substances rather than in the form of a copolymer. In other words, it is preferable that the conductive paste disclosed herein does not contain a copolymer of polyimide resin and silicone resin.

The conductive paste disclosed herein may contain other resin components within the range that does not impair the above-mentioned characteristics. Such resin components may be one or more of various known resin components such as rubber-based resins, polyester-based resins, epoxy-based resins, urethane-based resins, polyether-based resins, polyamide-based resins, and fluorine-based resins. However, among the known resin components, acrylonitrile-butadiene rubber (NBR)-based resins and acrylic-based resins may not be included because they do not have the effect of improving the adhesion resistance of polyimide resins like the above-mentioned silicone resins. In addition, from the viewpoint of differentiation from conventional conductive resin pastes, for example, the conductive paste may not contain epoxy-based resins or urethane-based resins. When the conductive paste contains other resin components other than polyimide resin and silicone resin, it is preferable that the proportion of these other resin components is 10 mass% or less (preferably 5% or less) in total.

(C) Organic Solvent As the organic solvent, any solvent that is compatible with the polyimide resin and the silicone resin can be used without any particular limitation. From the viewpoint of workability during film formation, storage stability, etc., it is preferable that the organic solvent mainly contains a high-boiling organic solvent having a boiling point of about 200° C. or more, for example, 200 to 300° C. (a component that occupies 50% by volume or more). Suitable examples of organic solvents include alcohol-based solvents having an -OH group, such as terpineol, texanol, dihydroterpineol, and benzyl alcohol; glycol-based solvents, such as ethylene glycol and diethylene glycol; glycol ether-based solvents, such as diethylene glycol monoethyl ether, butyl carbitol (diethylene glycol monobutyl ether), and triethylene glycol dimethyl ether; ester-based solvents having an ester bond group (R-C(=O)-O-R'), such as isobornyl acetate, ethyl diglycol acetate, butyl glycol acetate, butyl diglycol acetate, butyl cellosolve acetate, butyl carbitol acetate (diethylene glycol monobutyl ether acetate), γ-butyrolactone, and methyl benzoate; hydrocarbon-based solvents, such as toluene and xylene; aprotic polar solvents, such as N-methylpyrrolidone (NMP), and mineral spirits. Among these, from the viewpoint of suitably dissolving the above-mentioned resin components, organic solvents such as NMP and γ-butyrolactone can be preferably used. These may be used alone or in a suitable mixture of two or more.

The content of the organic solvent (C) is not particularly limited, but it is preferable that the content is approximately 70% by mass or less, typically 5 to 60% by mass, for example about 10 to 50% by mass, when the entire conductive paste is taken as 100% by mass. By satisfying the above range, it is possible to impart appropriate fluidity to the paste and improve workability during film formation. In addition, it is possible to improve the self-leveling properties of the paste and realize a conductive film with a smoother surface.

(D) Other Components The paste disclosed herein may be composed of only the above components (A) to (C), or may contain various additive components in addition to the above components (A) to (C) as necessary. As the additive components, those known to be usable in general conductive pastes can be appropriately used as long as they do not significantly impair the effects of the technology disclosed herein.

The additive components are broadly divided into inorganic additives (D1) and organic additives (D2). Examples of the inorganic additives (D1) include sintering aids, inorganic fillers, and glass frits. The inorganic additives (D1) have an average particle size of about 10 nm to 10 μm, and from the viewpoint of keeping the arithmetic mean roughness Ra of the conductive film small, it is preferable that the average particle size is, for example, 0.3 μm or less. Examples of the organic additives (D2) include leveling agents, defoamers, thickeners, plasticizers, pH adjusters, stabilizers, antioxidants, preservatives, colorants (pigments, dyes, etc.). The organic additives (D2) may or may not have an acid value. The content ratio of the additive components is not particularly limited, but may be about 20 mass% or less, typically 10 mass% or less, for example 5 mass% or less, when the entire conductive paste is taken as 100 mass%.

Such a paste can be prepared by weighing out the above-mentioned materials to a predetermined content ratio (mass ratio) and mixing them homogeneously. The materials can be mixed by using various conventionally known mixing and stirring devices, such as a roll mill, a magnetic stirrer, a planetary mixer, a disperser, etc. The paste can be applied to the substrate by using, for example, a chip dip method, a dispenser supply method, a printing method such as screen printing, gravure printing, offset printing, and inkjet printing, a spray coating method, etc. For the purpose of forming a resin electrode layer of an external electrode of a multilayer ceramic electronic component, for example, the dip method is suitable. For the purpose of bonding when mounting a multilayer ceramic electronic component on a substrate, for example, the dispenser supply method is suitable.

<Uses of paste>
The conductive paste disclosed herein can form a conductive film having excellent heat resistance and adhesiveness on any substrate. This conductive film is hardened by drying and constitutes a conductive film in an unfired state. Therefore, the paste disclosed herein can be preferably used as a conductive paste for forming a resin electrode layer of a ceramic electronic component that is vulnerable to temperature changes such as firing. In addition, it can also be used to form a conductive resin for bonding to replace solder when mounting a ceramic electronic component on a substrate.

In this specification, the term "ceramic electronic components" refers generally to electronic components that have an amorphous ceramic substrate (glass ceramic substrate) or a crystalline (i.e. non-glass) ceramic substrate. For example, chip inductors, high frequency filters, ceramic capacitors, low temperature co-fired ceramic substrates (LTCC substrates), and high temperature co-fired ceramic substrates (HTCC substrates), each of which has a ceramic substrate, are typical examples that fall within the meaning of "ceramic electronic components" herein.

Figure 1 is a cross-sectional view that shows a schematic configuration of a multilayer ceramic capacitor (MLCC) as a ceramic electronic component 1. The ceramic electronic component 1 typically includes a component body 10 and external electrodes 30 formed on a pair of opposing end faces of the component body 10.

The component body 10 has multiple internal electrodes 20 stacked with dielectric layers 12 between them. Each dielectric layer 12 is made of, for example, a laminated sintered body of ceramic green sheets containing a ceramic dielectric. In an actual MLCC, the dielectric layers 12 are integrated to such an extent that the joint boundaries between them are not visible. Here, a portion of the internal electrodes 20 is exposed at the end faces of the component body 10 (the left and right ends in FIG. 1).

The external electrode 30 is disposed on the outer surface of the component body 10. The external electrode 30 is formed on each of a pair of opposing end faces (left and right ends in FIG. 1) of the component body 10. The external electrode 30 has a first metal electrode layer 32, a conductive film (resin electrode layer) 34, a second metal electrode layer 36, and a third metal electrode layer 38.

The first metal electrode layer 32 contains copper (Cu), a base metal, as its main component, and is physically and electrically connected to the internal electrode 20. The first metal electrode layer 32 is formed continuously on a pair of left and right end faces of the component body 10 and the outer surfaces of the four side faces connected thereto. The first metal electrode layer 32 is formed by applying and baking a conductive paste containing Cu powder to a pair of end faces of the component body 10 and the outer surfaces of the four side faces connected thereto. The thickness of the first metal electrode layer 32 is, for example, 10 to 30 μm.

The conductive film 34 contains metal (Ag) powder as conductive particles, and is a layer formed by drying and hardening the conductive paste disclosed herein. The conductive film 34 is formed by applying and drying the conductive paste disclosed herein to a pair of end faces of the component body 10 and the outer surfaces of the four side faces connected thereto, leaving only the periphery of the first metal electrode layer 32. Here, the drying temperature is approximately 180°C or higher and 300°C or lower, although this may vary depending on the imide resin and silicone resin used. The thickness of the conductive film 34 is, for example, 20 to 100 μm. This allows the conductive paste disclosed herein to harden, forming the conductive film 34 as part of the external electrode 30.

The second metal electrode layer 36 contains Ni or a Ni alloy as a main component. The conductive film 34 is formed, for example, by Ni plating the surfaces of the first metal electrode layer 32 and the conductive film 34. The second metal electrode layer 36 has a thickness of, for example, 1 to 5 μm.
The third metal electrode layer 38 contains Sn or a Sn alloy as a main component, and is formed by plating the surface of the second metal electrode layer 36 with Sn or a Sn alloy. The third metal electrode layer 38 has a thickness of, for example, 1 to 5 μm.

In this manner, the ceramic electronic component 1 can be manufactured. Here, the external electrode 30 is electrically connected to the internal electrode 20 exposed on both end faces of the component body 10. This allows the current sent from the outside to the internal electrode 20 through one external electrode 30 to be stored and insulated in the MLCC without being sent directly to the other external electrode 33. When a current is passed through an external load, the charge stored in the MLCC is sent sequentially to the external circuit through the external electrode 30. At this time, the presence of the MLCC allows a stable supply of charge to the external circuit even when the power supply voltage is unstable. Such an MLCC includes a conductive film 34 with excellent heat resistance and adhesiveness on the external electrode 30. As a result, even if an electronic device equipped with an MLCC is exposed to a high-temperature environment such as a continuously moving vehicle and the substrate on which the MLCC is mounted is warped, the conductive film 34 adheres closely to the first metal electrode layer 32 and the second metal electrode layer 36, for example, cushioning the warping and enabling a stable electrical connection with the component body 10 to be maintained. This provides a ceramic electronic component 1 that is highly reliable even in a high-temperature environment. Although not specifically shown, the conductive paste can also be used as a bonding paste when mounting the ceramic electronic component 1 on a substrate.

The following describes some examples of the present invention, but it is not intended that the present invention be limited to those examples.

[Conductive paste]
Conductive particles, a resin component, and a solvent were mixed according to the formulations shown in Table 1 to prepare conductive pastes of Examples 1 to 19.
As the conductive particles, flake-shaped Ag powder (tap density 3.1 g/cm ³ ) with an average particle size of 4.7 μm was used in common in all examples. As the solvent, γ-butyrolactone was used in common. However, although not specifically shown, it has been confirmed that there is no significant difference in the tendency of the electrode characteristics described below even if the types of conductive particles and solvent are changed.

The ten resins shown in Table 1 were used alone or in combination as resin components. The resins shown in Table 1 are as follows. TD1, TD2, and TD5 below respectively represent the 1%, 2%, and 5% weight loss temperatures, and Tg represents the glass transition temperature.

"Polyimide resin 1": Solvent-soluble fluorine-containing polyimide resin (Tg: 360°C, TD1: 500°C, TD5: 540°C)
"Polyimide resin 2": Solvent-soluble polyetherimide resin (Tg: 260°C, TD1: 400°C, TD5: 450°C)
"Silicone resin 1": Addition curing silicone resin (two-component type)
"Silicone resin 2": Addition curing type silicone resin (one-component type)
"Silicone resin 3": Addition curing type silicone resin (phenyl silicone)
"Silicone resin 4": Condensation type silicone resin (flake-like)
"Silicone resin 5": Condensation type silicone resin (flake-like, different manufacturer's product from Silicone Resin 4)
"Silicone Resin 6": Addition-curing silicone rubber (room temperature curing type)
"Acrylic resin": Weight average molecular weight: 300,000, Tg: 56°C
"NBR resin": nitrile butadiene rubber, bound AN amount: 28.0, Mooney viscosity: 50

[Conductive films and their evaluation]
(Substrate Adhesion)
The conductive paste of each example was applied to the tip of two copper plates (2 cm x 5 cm, no surface treatment) with an area of 2 cm x 1 cm and a thickness of about 50 μm. The copper plate to which the conductive paste was applied was first dried at 180 ° C for 15 minutes and then at 280 ° C for 45 minutes to harden the conductive paste. This formed a conductive film of a predetermined dimension on the copper plate. Next, epoxy adhesive was applied to the conductive film portion of the two copper plates on which the conductive film was formed, and the copper plate portions were aligned so that they were positioned opposite each other, and the conductive films were superimposed and bonded together. This prepared a test piece for evaluating the substrate adhesion of the conductive film of each example.

The copper plate parts at both ends of the evaluation test piece were fixed to the upper and lower chucks of a tensile testing machine (Shimadzu Corporation, Universal Testing Machine Autograph), and a tensile shear test was performed according to JIS K6850:1999 (Test method for tensile shear adhesive strength of rigid adherends). In the tensile shear test, a tensile load (shear force) perpendicular to the adhesive surface of the evaluation test piece was applied at a predetermined loading rate, and the adhesive strength (shear strength) was measured from the tensile shear load (breaking force) when the evaluation test piece broke. The results are shown in the "Adhesion" column of Table ¹ , with adhesive strength of 6 N/mm2 or more as "A", 5 N/ ^mm2 or ^more and less than 6 N/ ^mm2 as "B", 4 N/ ^mm2 or more and less than 5 N/mm2 as "C", and less than 4 N/ ^mm2 as "D". Furthermore, for Examples 1 to 10, the relationship between the amount of silicone resin blended and the adhesiveness (adhesive strength) is shown in FIG.
The adhesive strength of the epoxy adhesive used to prepare the evaluation test pieces alone in a tensile shear test was 15 N/mm2 or ^more , and the epoxy adhesive portion did not peel off or break before the conductive film.

(Heat resistance)
The conductive paste of each example prepared was first dried at 180° C. for 15 minutes, then at 280° C. for 45 minutes, and then the weight loss rate was measured when it was held at 280° C. for 2 hours. The results are shown in the “Heat resistance” column of Table 1, with a weight loss rate of 3% or less rated as “OK” and a weight loss rate of more than 3% rated as “NG.”

[evaluation]
Examples 1 to 11 are examples in which the amount of silicone resin blended with the polyimide resin was changed in the range of 0 to 100 mass % to prepare a conductive paste. The conductive films obtained from the conductive pastes of Examples 1 to 11 all had a small weight loss rate of less than 3% when heated and held at 280°C, for example, and were confirmed to have heat resistance at 280°C.

As shown in Example 11, when a conductive paste is prepared using only silicone resin without blending polyimide resin, the adhesive strength of the formed conductive film is approximately 0 N/ ^mm2 , and such a conductive film has almost no adhesiveness to the substrate. Therefore, even if a conductive film (i.e., a buffer layer made of a resin conductive layer) in an external electrode of a ceramic electronic component is formed using such a conductive paste, the resin conductive layer and other external electrodes may easily peel off due to thermal shock or the like, leading to disconnection.
On the other hand, in Example 1, in which the conductive paste was prepared using only the polyimide resin without blending the silicone resin, the conductive film formed exhibits an adhesive strength of about 2 N/ ^mm2 due to the properties of the polyimide resin. However, this adhesive strength is less than 4 N/ ^mm2 , which is not sufficient to maintain the adhesion of each layer of the external electrodes in an environment where thermal shock is applied.

In contrast, it was found that blending a silicone resin into a polyimide resin changes the adhesiveness of the conductive film formed according to the blend ratio, as shown in Examples 2 to 10. That is, as shown in Figure 2, it was found that blending even a small amount of silicone resin into a polyimide resin improves the adhesive strength of the polyimide resin itself.
Also, it was found that the effect of improving adhesive strength was rapidly enhanced as the blended amount of silicone resin increased, as shown in Examples 2 to 6. This is thought to be because, whereas a conductive film containing a simple polyimide as a resin component has a relatively high rigidity and cannot follow the changes in a substrate (e.g., a copper layer that is the bottom layer of an external electrode) when it expands or contracts or moves due to, for example, thermal shock or external stress, the silicone resin suitably penetrates between the molecules of the polyimide resin, thereby imparting to the polyimide resin appropriate flexibility and adhesion and followability to the substrate.

However, as shown in Examples 6 to 10, it was found that the effect of improving the adhesive strength of the polyimide resin conductive film by the silicone resin tends to decrease when the ratio of the silicone resin is excessive. In other words, it is considered that the presence of an excess of silicone resin impairs the inherent adhesiveness of the polyimide resin.
From the above results, it was found that the proportion of the silicone resin blended with the polyimide resin should exceed about 2 parts by mass, be 3 parts by mass or more, preferably be 5 parts by mass or more, and more preferably be 10 parts by mass or more, when the polyimide resin and the silicone resin are taken as 100 parts by mass. It was also found that the proportion of the silicone resin blended with the polyimide resin should be about 50 parts by mass or less, be preferably 40 parts by mass or less, and more preferably be 30 parts by mass or less.

In Examples 5 and 12 to 18, as shown in Table 1, the resin components used in combination with polyimide resin 1 were changed to various types, such as silicone resins 1 to 6, acrylic resin, and NBR resin. With regard to the heat resistance of the conductive films formed from the conductive pastes of Examples 5 and 12 to 18, the weight loss rate was less than 3% in all examples, confirming that the films had sufficient heat resistance.

As shown in Examples 5, 12 to 16, it was found that when polyimide resin 1 and silicone resin were combined, a conductive film with excellent adhesion with an adhesive strength of 4 N/mm2 or ^more could be formed regardless of the type of silicone resin. In particular, when an addition-curing silicone resin was used as the silicone resin to be combined with the polyimide resin (Examples 5, 12 to 13), it was found that a conductive film with significantly excellent adhesiveness could be formed with an adhesive strength of 6 N/mm2 or more, which is greater than the adhesive strength of 4 N/mm2 ^{or more} and 5 N/mm2 or ^less when a condensation-type silicone resin (Examples 14 and 15) or a silicone rubber that is not a resin (Example 16) was used. Although the details are not clear, it is expected that the addition-curing silicone resin is more likely to crosslink in the polymer structure of the polyimide resin than a condensation-type silicone resin or silicone rubber, and is more likely to impart flexibility to the polyimide resin.

However, in Examples 17 and 18 in which acrylic resin or NBR resin was used as the resin component to be combined with the polyimide resin, the adhesive strength of the conductive film was less than 4 N/ ^mm2 , and it was found that a conductive film having sufficient adhesiveness could not be formed.
From the above, it was found that when a polyimide resin having high heat resistance is used for a conductive paste, the rigidity of the polyimide resin is relaxed by combining it with a silicone resin, and a conductive film having a softness, high adhesion to the substrate, and excellent adhesion can be formed. This realizes a conductive paste capable of forming a conductive film having both heat resistance and adhesion. It was found that the effect of relaxing the rigidity of the polyimide resin by the silicone resin is not exhibited in acrylic resin or NBR resin, but is an effect unique to the silicone resin. It was also found that such an effect is exhibited remarkably in silicone resins, particularly in resin-based silicone resins and addition-curing silicone resins.

Example 19 is an example in which the polyimide resin 1 in the conductive paste of Example 12 is changed to polyimide resin 2. A comparison between Example 12 and Example 19 shows that the same effect as above can be obtained even when the type of polyimide resin is changed.

The present invention has been described in detail above, but these are merely examples, and the present invention can be modified in various ways without departing from the spirit of the invention.

REFERENCE SIGNS LIST 1 Ceramic electronic component 10 Component body 20 Internal electrode 30 External electrode 32 First metal electrode layer 34 Conductive film 36 Second metal electrode layer 38 Third metal electrode layer

Claims (5)

Conductive particles;
A resin component,
An organic solvent;
Including,
the resin component comprises a polyimide resin and a silicone resin as a homogeneous blend of each other;
The silicone resin is an addition-curing silicone resin that is liquid at room temperature (25° C.) ,
The ratio of the polyimide resin to the liquid addition-curing silicone resin is adjusted to be 95:5 to 50:50 by mass. The conductive paste according to claim 1, wherein the resin component is contained in an amount of 10 parts by mass or more and 30 parts by mass or less when the conductive particles are taken as 100 parts by mass. The conductive paste according to claim 1 or 2, wherein the conductive particles include at least one of nickel, platinum, palladium, gold, silver, and copper. The conductive paste according to any one of claims 1 to 3, which is used to form an external electrode of a ceramic electronic component. a component body including a ceramic body and an internal electrode disposed within the ceramic body;
an external electrode provided on a surface of the component body;
Equipped with
A ceramic electronic component, wherein the external electrodes at least partially comprise a dried film of the conductive paste according to any one of claims 1 to 4.

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